1. Field of the Invention
The present invention relates to an exhaust secondary air valve, more particularly, an exhaust secondary air valve for a saddle-type vehicle including an engine disposed under a main frame and behind a down frame.
2. Background Art
Japanese Patent Laid-open No. Hei 6-270878 describes an exhaust secondary air system for feeding secondary air to an exhaust passage of an engine mounted on a saddle-type vehicle. Using this arrangement, a motorcycle is capable of oxidizing HC and CO contained in exhaust gas discharged from a combustion chamber of the engine into the exhaust passage.
The exhaust secondary air system described in the above document, which includes an air cleaner used for secondary air and a reed valve, is mounted on a bracket fastened to a mounting plate provided between right and left main frames positioned behind a head pipe of the motorcycle. An air outlet of the reed valve of the exhaust secondary air system is directed rearwardly of the vehicle. Accordingly, a secondary air feed pipe connected from a reed valve to an exhaust port of the engine extends slightly obliquely and upwardly from the air outlet of the reed valve to the rear side of the vehicle, being U-turned, and extends slightly obliquely and downwardly to the front side of the vehicle to be returned again to the vicinity of the reed valve. The secondary air feed pipe is then curved downwardly substantially at right angles, extending to the vicinity of the cylinder head of the engine, and further extends to be communicated to the exhaust port of the engine.